Eli5: how can you roll start a manual vehicle but not an automatic vehicle?

Question

Eli5: how can you roll start a manual vehicle but not an automatic vehicle?

In: Other

Answer 1

A manual has essentially a direct connection between the wheels and the engine when it’s in gear so turning the wheels turns the engine.

An automatic has a bit in between the engine and the wheels called a torque converter. It’s like a fan submerged in fluid and at low engine speed it makes it hard for the car to accelerate from a stop. Turning the wheels would only turn the outside of the torque converter and not the fluid enough to spin the fan and, in turn, the engine.